Conventionally, suggested is a format conversion for converting a 525i signal as a standard definition (SD) signal into a 1050i signal as a high definition (HD) signal. The 525i signal means an image signal in an interlace system consisting of 525 lines. The 1080i signal means an image signal in an interlace system consisting of 1080 lines. FIG. 14 shows a positional relationship between the pixels of the 525i signal and the pixels of the 1080i signal. Herein, large dots are pixels of the 525i signal, and small dots are pixels of the 1080i signal. Solid lines express the positions of pixels in odd fields and broken lines express the positions of pixels in even fields. When the 525i signal is converted into the 1050i signal, it is required to obtain four pixels of 1050i signal in correspondence with one pixel of 525i signal in the respective odd and even fields.
Conventionally, in order to perform the above format conversion, it has been suggested that, when the pixel data of 1050i signal is to be obtained from the pixel data of 525i signal, coefficient data of an estimated equation corresponding to a phase of each pixel of 1050i signal with respect to the pixel of 525i signal is stored in a memory and then, the pixel data of 1050i signal is obtained according to the estimated equation using the stored coefficient data.
According to the method described above where the pixel data of the 1050i signal is obtained from the 525i signal according to the estimated equation, the resolution of an image produced by the 1050i signal is fixed. Therefore, it has been impossible to obtain desirable resolution in accordance with the contents of an image and the like, like conventional adjustments of contrast, sharpness and so on.